1. Technical Field
The present invention relates in general to reduced sidelobe antenna array assemblies, and in particular to low profile antenna array assemblies for use in cellular communications having low visual profile site capabilities when mounted against a building surface.
2. Description of the Related Art
In cellular communications it is common practice to utilize a three (3) sector antenna configuration for a given base station where a sector refers to the area coverage provided by the beamwidth of the main beam (also known as the mainlobe) of the antennas' radiation pattern. The use of pointing the mainlobe of an antenna for a given sector has produced significant advantages in modern day cellular system technologies. More specifically, sectorization reduces co-frequency interference, allowing more efficient frequency planning and the associated capacity improvements in Advanced Mobile Phone Systems (AMPS), Time Division Multiplexed Access (TDMA), and Global System Mobile Communications (GSM) systems. Additionally, for Code Division Multiplex Access (CDMA) cellular systems, there is a direct capacity increase associated with each new sector.
However, when considering utilizing more than three (3) sectors of coverage, the additional sectors increase in capacity is not as efficient due to overlapping coverage from the antennas' radiation pattern into the additional sectors. More particularly, current beamwidth cellular antennas produce significant sidelobes, which in turn scatter energy into the adjacent sectors, and effectively reduce the capacity efficiency of these additional sectors. In most cases, the sidelobe peak gain is within twelve (12) dB of the main beam peak gain and in many cases the sidelobes gain can be five (5) to six (6) dB below the mainlobe gain of the antenna which from a system performance standpoint may be unacceptable.
Furthermore, cellular antenna assemblies are quite large due to current antenna design constraints when designing in the cellular phone frequency range of 800 Mhz and 1900 Mhz. This results in antennas being installed in urban areas and onto buildings with bulky and unsightly installation hardware such as long masts. Additionally, current antennas are designed with fixed radiation patterns having the main beam at boresight resulting in complicated and expensive mounting brackets that must incrementally swivel in the horizontal and vertical planes to achieve the sector coverage desired.
Because of the continued widespread use of cellular communications, it is desirable to implement relatively narrow beamwidth sectored antenna configurations having low sidelobes for cellular phone applications in the 800 MHz and 1900 MHz bands with minimal coverage overlap between sectors. Additionally, it is desirable to have a low profile antenna that can be electronically scanned thereby eliminating the need for pointing bracketry and that can be flush mounted and camouflaged against a building surface making it virtually invisible to observers at any significant distance. The subject invention herein solves all these problems in a new and unique manner which has not been part of the art previously.